Daniel Kammen is a Professor of Energy in the Energy and Resources Group at the University of California, Berkeley. As a renewable energy expert he was appointed as a science envoy to the State Department during the Obama administration. He came into the public eye when he resigned in August of 2017, citing President Trump's response to the violence in Charlottesville as the final straw that led to his departure. In his resignation letter which he posted to Twitter, Kammen wrote that Trump's remarks about the racial violence in Virginia had attacked “core values of the United States.” In his resignation, the first letter of each paragraph spelled out I-M-P-E-A-C-H.

Photographed at his home in Berkeley for El País